How do concerns about terrorism affect the way Americans view the 2008 presidential candidates? How would an event that increases the prominence of terrorism, like a threat or attack, affect the 2008 election? Past theory and research are ambivalent on these questions. In this paper we empirically investigate the effects of exposure to a journalistic account of an imminent terror threat in a national (N = 1,282), internet-based field experiment. Overall, we find that exposure to terror threats increased concerns about "homeland security" without affecting candidate preferences. However, analysis of politically moderate respondents - a substantial subset of the total sample (40%) with a high rate of undecided, likely voters - showed that this group expressed significantly lower support for Senator John McCain when exposed to the terror threat than in the control condition. These findings converge with past research suggesting that Americans' views of the war on terror have changed significantly (Davis and Silver 2004) and that terror threats may serve as "anti-rally" events for candidates with unpopular foreign policies, especially among moderate or undecided voters (Bali 2007). We conclude by proposing a more general model of the effects of external threats on leader preferences suggested by past and present research.